The invention relates to a plastic tank, in particular a fuel tank of a motor vehicle, having a media-carrying line. Furthermore, the invention relates to a process for the production of such a plastic tank.
Plastic tanks of this kind, designed as fuel tanks, are used in modern motor vehicles and are therefore known. They comprise media-carrying lines, which currently have to be inserted into the container interior and fastened therein via a filling opening or via special assembly openings after the tank has been produced. For example, a line has to be disposed in the region of the tank bottom of the fuel tank as an intake line for a fuel pump. In order that an adequate supply of fuel is ensured under all possible operating conditions, this line must lead to the deepest point of the fuel tank and also should not alter its position when the vehicle is being driven. With the present plastic tanks, this can be achieved only with relatively great expenditure, so the production of such tanks is expensive. Nevertheless, there is the risk of the position of the installed parts altering during adverse driving conditions and then, for example, no more fuel is taken in before the fuel tank is really empty. Plastic tanks of this type are often produced by the blow-moulding process. In this process, a freshly extruded pipe is subjected to internal pressure in a hollow mould, so that its wall comes to bear against the wall of the hollow mould. This process has the disadvantage that particular formations of the interior are possible only to a very restricted extent, in particular no fixed line internals can be realized.
If it is wished to mould components onto the inside wall of an injection-moulded tank, up until now such tanks have been created from at least two shells produced by the injection-moulding process. For producing each shell, use is made of a hollow mould into which an inner mould engages in such a way that only the regions which are to form the wall and any moulded-on components after the injection of the plastic remain free. Even in the case of such an injection-moulding process, until now it has not been possible to make components provided in the interior of the plastic tank of a hollow form.
In the case of a known process for producing plastic injection mouldings (EP 0 745 468), a hollow body is created by filling the cavity of a hollow mould with injection moulding compound and subsequently subjecting the mould cavity to compressed gas (internal gas pressure technique). In this process, the still soft injection moulding compound is pressed against the inner side of the injection mould. Once the injection moulding compound has solidified on the mould wall, the gas is discharged via a duct and a switchable valve. As this happens, the gas flow tears into the wall of the plastic container an outwardly leading outlet. This serves merely for faster discharge of the compressed gas. It cannot be used to create an interior material projection or a cavity profile parallel to a tank wall.
One disadvantageous aspect of the process described is that at least two further openings are required in the wall of the integral hollow body for filling it with and emptying it of gas. These openings must be closed in a further operation. A further disadvantageous aspect is that, with the process described, no further components can be arranged in the interior of the hollow body, for example lines along an inside wall, without breaking through the wall of the surrounding tank. Lines required internally would have to be laid and fixed in an additional operation, as in the case of the prior art mentioned at the beginning, necessitating a large number of connecting elements between the sections of line and fastening elements.
The invention is based on the problem of developing a plastic tank of the type mentioned at the beginning which can be produced at low cost and in which the position of lines built on or in is reliably fixed. Furthermore, a process for the production of such a tank is to be specified.
The first-mentioned problem is solved according to the invention by at least one section of the media-carrying line being moulded onto a wall of the plastic tank. This may lie on the inside or outside and/or penetrate the wall.
Such a plastic tank according to the invention requires only a small number of connecting elements on account of the lines integrally formed with the wall of the plastic tank. By dispensing largely with assembly work, the plastic tank can be produced at particularly low cost. Furthermore, the integral design achieves the effect that the lines are inevitably fixed in their position and cannot alter their position. Therefore, the plastic tank according to the invention is particularly suitable as a fuel tank. Use as a fuel tank is appropriate because of the large number of lines, in particular fuel, air-admitting and venting lines in the interior of the fuel tank, which are intended to ensure an adequate supply of fuel to the engine even on steep inclines and when there are great variations in temperature, while at the same time meeting high safety requirements.
Furthermore, fuel must not escape either in the event of an accident or by permeation. The special nature of the plastic tank according to the invention makes this possible. It has regions of high rigidity and regions of high elasticity. At the same time, the number of connecting elements is reduced.
In the case of the plastic tank according to the invention, the lines can also be provided where their subsequent assembly was not possible, or only with very great expenditure, in the case of the previous plastic tanks. Finally, the possibility of lines being incorrectly routed due to assembly errors is ruled out.
Furthermore, the mechanical properties of the plastic tank can be improved in a particularly beneficial way by the direct, reinforcing attachment of the line to the wall of the plastic tank. In particular, the strength of the wall can be increased many times over in partial respects by the specifically selected design of the line and its routing parallel to a wall.
The effect of improved mechanical properties can be additionally increased significantly if the media-carrying line is moulded onto the plastic tank with a web interposed. The effect of the rib-like reinforcement formed by a web brings about a considerable increase in the wall rigidity of the plastic tank in the partial region concerned. The web may in this case perform further functions, such as for example influencing the direction of flow in the line or else serve assembly purposes.
The mechanical properties can be influenced in a particularly advantageous way in any desired sections of the line if the web has at least one aperture. The rigidity reduced in this region allows in particular the design of a plastic tank with particularly elastic properties. Consequently, a plastic tank which has high rigidity in some partial regions but at the same time can be elastically deformed particularly well in other partial regions can be realized. In the region of any undercuts of the web with respect to the line cross-section, the mould will be made with corresponding divisions.
A further exemplary embodiment of the invention, in which the web varies in thickness or height in different regions over its length, permits a largely free design of the line. As a result, even with the line following an essentially planar path, it is possible for example for specifically selected stiffening to be realized by reinforcing the web. In particular, the requirements for the flow behaviour of the medium carried in the line can be taken into account in this case without influencing the stiffening effect. It is also easily possible in particular for inclines or slopes with fixed angles of inclination to be represented.
Depending on what is required, it is important that the plastic tank is not stiffened by attached components. This is the case, for example, if the plastic tank is exposed to deforming forces, and therefore must be elastically deformable. One particular embodiment of the invention meets such requirements if the line is attached to the plastic tank only in the region of a connection opening. In this case, the line runs largely freely in the interior and is connected to the wall of the plastic tank only where it penetrates the wall, or is connected to a connection element. In this way, an absolutely sealed lead-through of the line is created right at the original moulding stage of the tank.
Another particularly advantageous development of the invention is provided by a connecting element being moulded onto the media-carrying line. As a result, the assembly expenditure can be reduced, since it is possible to dispense with the laborious subsequent fastening of separate connecting elements. Further connection elements can therefore be connected to the line without any problem, for example by means of a connecting element designed as a plug-in connection. In this case, incorrect assembly is at the same time largely ruled out.
A particularly favourable embodiment is provided in this case by the connecting element having a plug to be positively connected to a coupling. The positive connection produces a largely sealed connection, which may, for example, also be made releasable. It is also possible in this case to provide an amount of tolerance such that axial mobility is achieved. It is thus possible to compensate for both production tolerances and operationally induced deformations of the plastic tank and therefore prevent in particular these from causing the connecting element to be damaged or to leak.
It is also advantageous if the connecting element is designed for the connection of a sucking jet pump. The sucking jet pump, to be introduced into the plastic tank as a separate component, may therefore, as a largely pre-fabricated component, be already equipped with a corresponding coupling element, so that the sucking jet pump can be inserted directly into the plastic tank. In this case, the sucking jet pump can be easily connected by virtue of the integrally moulded-on connecting element and the resultant, largely stiff type of design, since the connecting element does not have to be additionally fixed for this purpose.
It is also particularly appropriate in this case if the connecting element is designed at the same time for fixing a connected component. As a result, the connecting element may serve simultaneously for the connection of the component to the media-carrying line and also for its positioning. This dispenses with the need for further fixing means and reduces the assembly expenditure.
A development of the invention is particularly favourable if the media-carrying line is arranged in a first half-shell of the plastic tank and the connecting element is designed for the connection of a further media-carrying line, arranged in a second half-shell. As a result, the lines arranged in two initially separate half-shells are connected to each other at the same time as the half-shells are joined together to form the plastic tank. The lines may in this case also be arranged in particular in a way which is not dependent on subsequent accessibility to the interior of the plastic tank. It is hence possible to dispense with the assembly openings otherwise required for this purpose, so that a much-simplified design of the plastic tank can be achieved.
The second-mentioned problem, that is of providing a process for the production of a plastic tank, in particular a fuel tank of a motor vehicle, which comprises a media-carrying line connected in certain sections to its wall, is solved according to the invention by the plastic tank comprising two half-shells respectively produced by the injection-moulding process in a hollow mould by means of an inner mould inserted in the latter and designed as a core, a shaping of the mould having the effect that along one wall of the plastic tank at least one sprue body is moulded on in one piece with the tank wall or is integrally connected to it, and by this body subsequently being formed into a hollow body, forming the line, by feeding in and carrying away a pressurized gas via channels of the mould by means of the internal gas pressure technique. Material accumulations away from the contact surfaces between the injection moulding compound and the mould cool down relatively more slowly and can consequently still be removed.
In the case of this process according to the invention, the injection moulding process, known per se, and the customary internal gas pressure technique are combined with each other in a particularly advantageous way and used for producing even internal lines. The half-shell is created by filling the space between the hollow mould and the inner mould with injection moulding compound.
The tanks in question are mass-produced parts. Therefore, even relatively high expenditure in mould making is comparatively cheaper than the operations for subsequent installation of the lines, in particular with regard to the distinct reduction in the failure rate. By application of the process according to the invention, all the required lines in the interior can be moulded on directly in a single operation. This dispenses with additional working steps for the assembly and connection of the lines. Furthermore, the integral or one-piece design overcomes various sealing problems.
In a development of this process, the outer surface or surrounding area of the said sprue body is preferably cooled in the mould, in order that its outer wall solidifies preferentially before the compressed gas is blown into the corresponding mould channels and the core of the sprue body is blown out along the desired path. It is also of advantage that, according to a development, the mould or the profile of the hollow space in the sprue body may be made not only rectilinear but also angled or curved.